As is known, optical and electromagnetic tracking (EMT) technologies are two non-mechanical, real-time, approaches for accurate medical instrument tracking and navigation using appropriately registered volume images (digital data sets). Both optical and electromagnetic technologies have advantages and limitations, but on balance the technological advantages of EMT for minimally invasive procedures are dominant. In particular, EMT is believed to be the preferable technology because of the ability to track objects inside the body (beyond line-of sight) and the compact size of the tracked sensors. These powered sensors typically provide position and orientation data sets of 5 or 6 degrees-of-freedom (DOF) and combined with the electronic cables required are relatively expensive.
EMT systems that support image fusion and instrument tracking are commercially available and some are disclosed in the patent literature. They typically enable determination of 5 or 6 DOF orientation and position of an instrument, such as a needle, by determining location, orientation, and/or positioning information relative to some coordinate system. For example, Ascension Technology Corporation makes 5 and 6 DOF position and orientation tracking devices suitable for various medical applications, e.g., to navigate, localize, and guide medical instruments for image-guided procedures. Other manufacturers/suppliers of EM tracking systems include Polhemus, Inc., Northern Digital Inc. and Medtronic, Inc. Suppliers of software, tracked needles and other instruments for clinical use that utilize these technologies in medical procedures include Traxtal Corporation, Veran Medical and Medtronic, Inc. Image fusion in combination with ultrasound is available from Traxtal, Inc., GE Healthcare Ultrasound and Esaote Ultrasound, among others.
Typically these tracking systems use the attenuation of oriented electromagnetic signals to determine the absolute position and orientation of a sensor, relative to a source, e.g., a magnetic field generator. The source and the sensor typically are connected via cables to an electronics module, which contains a microcomputer and associated electronics of the system. The source typically includes three orthogonal coils that are pulsed in rotation, one after another. Each pulse transmits a radio frequency electromagnetic signal that is detected by the sensor. The sensor also contains two or three orthogonal coils, which measure the strength of the signal from the current source coil. By using the known pulse strength at the source and the known attenuation of the strength with distance, the position and orientation of the sensor coils can be calculated by the system via triangulation techniques.
External markers are commonly used to identify surface (skin) locations on a patient during image-guided medical procedures. These markers typically attach with adhesive and are seen as a point, a series of points, or a grid by the imaging technology being used. Some markers are “seen” by only a single imaging modality (e.g., x-ray), while others may be well seen in multiple modalities (e.g., CT (x-ray) and MR). Surface markers of this type can also be used to assist with 3-D image fusion, where a 3-D image data set is acquired in one modality (e.g. CT) and then fused with a 3-D data set from another taken earlier (e.g., MR), or fused in real time with 2-D data sets, such as ultrasound, to facilitate the targeting of lesions within the body. In these cases the markers may be used as points of reference to help align or register the image data sets. Accurate registration is critical to achieving useful image fusion, and the greater the number of common points that are in a known position on both data sets, and the more accurate these known positions, the greater the accuracy and usefulness of the fused images. Attaching 5 or 6DOF electromagnetic sensors to surface markers in a known orientation permits registration of a 3-D imaging data set that includes these markers with the electromagnetic field of an electromagnetic navigation system. Specifically, one 6DOF sensor associated with at least 4 markers that are not coplanar, or two 5DOF sensors that are associated with at least two markers each that are oriented so as to avoid being co-planar can provide 3-D registration. Such markers are being used in currently available electromagnetic navigation medical systems. However, two problems are not addressed by these devices. One is the expense created by having the relatively expensive electromagnetic sensors and cables permanently embedded in these component markers that must be disposed of after a single use to avoid patient-to-patient contamination. The second is the inability to place, remove and then replace the marker in the same location on a patient at a different time. This can be critical to the marker's use for registration because the best images for visualizing a tumor or other internal lesion, in many cases, may be obtained at an initial diagnostic or treatment planning imaging procedure (e.g., CT, PET-CT or MR scan) that is not concurrent with the therapeutic procedure.
A need exists for a marker device, which allows inclusion of an EM sensor, which also can be readily and reproducibly secured to the body of a patient for use, and which may be disposable, but will enable the reuse of the sensor, since that component is relatively expensive.
The subject invention addresses that need by providing an active marker device that includes disposable (e.g., one-time use) components that is releasably and reproducibly secureable to the skin of the patient while permitting re-use of the much more expensive sensor assembly. Since the sensor assembly is a significantly expensive component of an EMT system, the subject invention enables users to greatly reduce costs per procedure in the rapidly expanding market for image fusion and guidance. While re-using the expensive 5 or 6 DOF powered (active) EM sensors will require a more complex setup and assembly process for each use, the payoff in reduced cost per procedure is believed to be so critical that the small extra time required for such set-up will likely be gladly tolerated.
Moreover, the subject invention is designed with a universal approach allowing it to be used across all OEM imaging platforms. In particular, it is anticipated that the subject invention will be utilized by physicians in the following specialties: interventional radiology, radiology, surgery and cardiology. Anticipated clinical applications are biopsy procedures, ablation procedures, catheter placements, intravascular procedures and endoscopic procedures.
The present invention basically comprises a device that is easily attached to the skin and easily removed via plural releasably securable attachment members, e.g., adhesive disks, each creating a respective attachment point. These attachment points are oriented like a tripod with sufficient spacing to produce a stable position and orientation on the patient's skin surface. Moreover, the device also includes a frame assembly which contains four visualizable elements establishing four respective reference points that are readily seen in CT and/or MR imaging and which do not interfere with the images. The four reference points are unequally spaced and are not coplanar, the combination of which facilitates software identification and orientation within any 3-D image set that includes the four points. The frame assembly also includes a receptacle or socket for releasably receiving a 6DOF electromagnetic sensor. That sensor is contained in a shaped housing and when releasably mounted in the socket is in a single, reproducible orientation. The socket itself is in a fixed and known orientation to the four reference points. The sensor's electrical components are located in a calibrated location within the sensor's housing. Thus, the 6DOF sensor has a known, fixed relationship to the four reference points and can be inserted to a stable position and removed as required.
Also, the frame assembly of the marker device, in addition to having a “tripod” set of legs that support it and the adhesive attachments, has three, asymmetrically spaced holes or apertures in a common plane in the base portion of the frame assembly. These apertures allow the operator to mark or “tattoo” the patient's skin with visible indicia using the singular orientation of the device's frame assembly. The marker device of this invention can then be placed at the time of an imaging exam and within the field being imaged. The skin can be marked using these three apertures as a guide for accurate future re-placement of an identical marker. Then, if the patient is in the same basic physical position at this subsequent procedure, any new images obtained in the region of the marker may be more quickly and accurately fused to the earlier image data to take advantage of any additional information that may be present. Thus, for example: if this marker was placed on the skin in the region of the liver at the time of a diagnostic CT performed with IV contrast with the patient in supine position, and a lesion was demonstrated in the liver that could only be seen with IV contrast, then, if the patient was to have a subsequent percutaneous biopsy or ablation of this lesion in the supine position, an identical marker could be re-placed on the skin in the same position and be used as a reference to register the location of this lesion in the liver on new CT images obtained at this later time without the need for additional IV contrast to illuminate it.
All references cited and/or identified herein are specifically incorporated by reference herein.